1. Technical Field
The present invention relates generally to data flow control over a network and more particularly to a communications scheduler controlling data flow over a network.
2. Description of Related Art
As transmission of network data over a communications network has become commonplace, users increasingly rely upon the speed and accuracy of network data transferral. One of the most common protocols to transmit network data is the transmission control protocol/internet protocol (TCP/IP). The TCP/IP protocol, like many protocols, organizes network data into packets and controls the transmission of packets over the communications network.
Slow-start is a part of the congestion control strategy of the TCP/IP protocol. Slow-start is used to avoid sending more packets than the communications network is capable of handling. Slow-start increases a TCP congestion window size until acknowledgements are not received for some packets. The TCP congestion window is the number of packets that can be sent without receiving an acknowledgment from the packet receiver. Initially, packets are slowly sent over the communications network. Transmission of the packets is increased until the communications network is congested. When acknowledgements are not received, the TCP congestion window is reduced. Subsequently, the number of packets sent without an acknowledgement is reduced and the process repeats.
The TCP/IP protocol can allocate bandwidth that is roughly inversely proportional to the long round trip time (RTT). Although many people generally expect bandwidth to be equally shared among users, the bandwidth is often in relation to the RTT ratio. In one example, two different users may be transmitting data. The first user may desire to transmit data to a local digital device with a 1 ms round trip time while the other user may desire to transmit data to another state with a 100 ms round trip time. The standard TCP/IP protocol will, on average, deliver 100× more bandwidth to the local device connection than to the out-of-state connection. The TCP/IP protocol does not consciously try to enforce any kind of explicit fairness policy. As a result, users that transmit data locally may receive better service at the unfair expense of those wishing to transmit data over longer distances.
FIG. 1 is a block diagram of a computer 100 configured to transmit network data in the prior art. The computer 100 depicts hardware and software elements related to transmission of network data. Other hardware and software of the computer 100 are not depicted for the sake of simplicity. The computer 100 comprises an application 110, a TCP/IP stack 120, a network device driver 130, and a network interface card 140. The network interface card 140 is coupled to a communications network over a link 150. The computer 100 can be any digital device configured to transmit network data.
The TCP/IP stack 120 receives the network data from the application 110 and proceeds to organize the network data into packets. Depending on the type of network, a packet can be termed a frame, block, cell, or segment. The TCP/IP stack 120 buffers the network data prior to organizing the network data into packets and subsequently buffers the packets.
The network device driver 130 enables an operating system of the computer 100 to communicate to the network interface card 140. The network interface card 140 is any device configured to send or receive packets over the communications network. The network device driver 130 configures the network interface card 140 to receive the packets and subsequently transmit the packets over the link 150 to the communications network.
In one example, the TCP/IP stack 120 of the sending computer 100 will not send another packet across the communications network until an acknowledgement from the destination is received. The number of packets between acknowledgments increases until a packet is lost and an acknowledgment is not received. At which point the TCP/IP stack 120 slows down the transmission of packets and, again, slowly increases the speed of transmission between acknowledgments until, again, a packet is lost. As a result, the transmission of network data by the TCP/IP stack 120 can be graphed as a saw tooth; the transmission of network data increases until packets are lost and then transmission drops to a slower speed before repeating the process. Under the TCP/IP approach, packets are often transmitted at speeds below the network's capacity. When the packets are not being sent slowly, however, the communications network quickly becomes congested and the process repeats.
While the TCP/IP stack 120 waits to transmit the packets, the packets are buffered. If the TCP/IP stack 120 transmits too slowly, the buffers may overrun and packets may be lost. Further, the process of buffering and retrieving the buffered packets slows packet transmission and increases the costs of hardware.
The TCP/IP stack 120 delivers different performance depending on the distance that packets are to travel. The TCP/IP stack 120 generates packets based on received network data. The destination of the packets dictates the order in which the packets are transmitted. Packets to be transmitted longer distances may be transmitted slower than packets to be transmitted shorter distances. As a result, this procedure may not be fair to users wishing to transmit mission critical data long distances.
Performance enhancing proxies have been used to improve performance of local networks by overriding specific behaviors of the TCP/IP stack 120. In one example, individual digital devices on a local area network are configured to transmit packets based on a proxy protocol. The proxy protocol overrides certain behaviors of the TCP/IP stack 120 to improve the speed of transmission of network data. However, the performance enhancing proxy does not find bottlenecks on networks, control the transmission of network data based on bottlenecks, nor improve fairness in packet transmission.